1. Field of the Invention
The present invention relates to a function expansion unit preferably used in a portable computer and, more particularly, to a function expansion unit having a function of supplying a power to a computer.
2. Description of the Related Art
In a personal computer field, a laptop or book-type portable personal computer having a light weight and a small size has prevailed, and has been frequently used as a low-end machine. The laptop personal computer cannot support many functions as standard functions to maintain good portability of the computer. A high-grade function is generally presented as an optional function. More specifically, a high-grade function is presented as a function expansion card (to be referred to as only an expansion card or a circuit board hereinafter), and the expansion card is inserted into the vacant slot of a function expansion unit (to be referred to as only an expansion unit hereinafter) to be connected to the personal computer, thereby obtaining the high-grade function.
An expansion unit capable of supplying a power to a personal computer is disclosed in, for example, U.S. patent application Ser. No. 578,533 and European patent application 90117214.8. The contents of the U.S. and European patent applications are incorporated as a reference in this specification. Personal computers driven by a battery are generally used, and power supply from the expansion unit to the personal computer is performed in a DC manner.
However, when an expansion circuit board itself has high power consumption, or when a plurality of expansion circuit boards are arranged in a personal computer, total power consumption may exceed a power which can be supplied by an expansion unit. This may cause the erroneous operation or breakdown of the personal computer.